Method for controlling an engine with an EGR system

ABSTRACT

A method for controlling an internal combustion engine ( 10 ) is provided. The engine ( 10 ) includes an exhaust gas recirculation (EGR) system ( 18, 20 ). The method includes determining an air mass flow rate through the intake manifold at a location upstream of the exhaust gas introduction, and determining an engine volumetric efficiency based on an engine speed and an intake manifold air density. An EGR flow rate is determined based on the volumetric efficiency, the intake manifold air density, an engine displacement volume, the engine speed, and the intake manifold air mass flow rate. The engine ( 10 ) is controlled based on the EGR flow rate. Preferred techniques for determining engine volumetric efficiency and EGR flow rate are also provided.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

This invention was made with United States Government support, and theUnited States Government has certain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for controlling an internalcombustion engine including an exhaust gas recirculation (EGR) system.

2. Background Art

In the control of internal combustion engines, the conventional practiceutilizes an engine controller with inputs, outputs, and a processor thatexecutes instructions to control the engine including its varioussystems. The engine may include a variable geometry turbocharger (VGT)system and an exhaust gas recirculation (EGR) system. U.S. Pat. No.6,305,167 describes an existing method of controlling an engine. Theengine business is quite competitive. Increasing demands are beingplaced on manufacturers to provide improved performance, reliability,and durability while meeting increasing emissions requirements.

An EGR system introduces a metered portion of exhaust gases through anEGR valve into the intake manifold of the engine. The exhaust gaseslower combustion temperatures to reduce the level of oxides of nitrogen(NO_(x)) that are produced. The EGR valve itself may take any suitableform such as a butterfly valve. The EGR system has been used on manyengines, including heavy-duty diesel engines. Sometimes, these heavyduty diesel engines employ a turbocharger system such as a variablegeometry turbocharger (VGT) system in addition to the EGR system.

Exhaust gas recirculation (EGR) is considered one of the enablingtechnologies for reduction of NO_(x) emission in diesel engine exhaust.And the reduction of NO_(x) using EGR usually comes with an increase inparticulate matters (PM) emission. To achieve the best trade-off ofNO_(x), vs. PM, precise engine control, including the control of EGRflow rate especially, is critical. The control strategy for dieselengines equipped with EGR requires time-averaged EGR flow rate as aninput parameter and the current technology is to use an orifice orventuri type of flow meter in the EGR circuit to directly measure EGRflow rate. Because the EGR flow, usually taken from turbo housing orexhaust manifold, is highly pulsating, it is a technical challenge toobtain accurate EGR flow rate measurement and its time averaged value.In addition, the flow meter increases the flow restrictions in the EGRcircuit and could also be contaminated by the soot-containing EGR flow,resulting in loss of accuracy or even sensor malfunction.

For the foregoing reasons, there is a need for an improved method forcontrolling an engine.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide animproved method for controlling an engine with an EGR system in whichEGR flow rate is determined without direct measurement of it in the EGRcircuit.

In carrying out the above object, a method for controlling an internalcombustion engine is provided. The engine includes an engine blockdefining a plurality of cylinders, an intake manifold for supplying airto the plurality of cylinders, a controller, and an exhaust gasrecirculation (EGR) system. The EGR system introduces a metered portionof exhaust gases to the intake manifold. The controller communicateswith the EGR system to control the engine. The method comprisesdetermining an air mass flow rate through the intake manifold at alocation upstream of the exhaust gas introduction. The method furthercomprises determining an engine speed, determining an intake manifoldair density, and determining an engine volumetric efficiency. The enginevolumetric efficiency is based on the engine speed and the intakemanifold air density. The method farther comprises determining an EGRflow rate based on the volumetric efficiency, the intake manifold airdensity, an engine displacement volume, the engine speed, and the intakemanifold air mass flow rate. The method further comprises controllingthe engine based on the EGR flow rate.

Further, in carrying out the present invention, an internal combustionengine is provided. The engine includes an engine block defining aplurality of cylinders, an intake manifold for supplying air to theplurality of cylinders, a controller, and an exhaust gas recirculation(EGR) system. The EGR system introduces a metered portion of exhaustgases to the intake manifold. The controller communicates with the EGRsystem to control the engine. The controller is programmed to controlthe internal combustion engine by determining an air mass flow ratethrough the intake manifold at a location upstream of the exhaust gasintroduction. An engine speed and an intake manifold air density aredetermined. An engine volumetric efficiency is determined based on theengine speed and the intake manifold air density. An EGR flow rate isdetermined. The EGR flow rate is based on the volumetric efficiency, theintake manifold air density, an engine displacement volume, the enginespeed, and the intake manifold air mass flow rate. The engine iscontrolled based on the EGR flow rate.

It is to be appreciated that methods and engines of the presentinvention may utilize a wide variety of techniques to determine theintake manifold air mass flow rate, and the engine may include avariable geometry turbocharger (VGT) system. Suitable air mass flow ratedetermination techniques include hot-wire or hot-film based techniquesat the compressor inlet to measure fresh charge air flow, as well asequivalent techniques that, for example, make determinations based onpressure and temperature during the stable flow process at thecompressor.

In one embodiment, determining the engine volumetric efficiency furthercomprises determining an engine exhaust to intake pressure ratio. Acorrection factor based on the engine exhaust to intake pressure ratiois determined. The engine volumetric efficiency is further based on thecorrection factor.

In another embodiment, determining the engine volumetric efficiencyfurther comprises establishing a neural network. The neural networkreceives the engine speed, an intake manifold air pressure, an intakemanifold air temperature, and an exhaust pressure as inputs, andprovides the engine volumetric efficiency as an output.

Preferably, determining the EGR flow rate further comprises determiningthe EGR flow rate according to

{dot over (m)} _(EGR)=η_(v)ρ_(a,i) V _(d) N/2−{dot over (m)} _(charge)

where η_(v) is the engine volumetric efficiency, ρ_(a,i) is the intakemanifold air density, V_(d) is the engine displacement volume, N is theengine speed, {dot over (m)}_(charge) is the intake manifold air massflow rate, and {dot over (m)}_(EGR) is the EGR flow rate. This equationis applicable for a 4 cycle internal combustion engine and would bemodified if applied to a 2 cycle internal combustion engine.

The above object and other objects, features, and advantages of thepresent invention are readily apparent from the following detaileddescription of the preferred embodiment when taken in connection withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that illustrates an internal combustion engine withVGT and EGR systems in the preferred embodiment of the presentinvention;

FIG. 2 illustrates a method for controlling an internal combustionengine;

FIG. 3 illustrates an embodiment utilizing a correction factor; and

FIG. 4 illustrates an embodiment utilizing a neural network.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates an internal combustion engine including an engineblock 10 defining a plurality of cylinders, with each cylinder receivingfuel from a fuel injector. In a preferred embodiment, the internalcombustion engine is a compression-ignition internal combustion engine,such as a heavy duty diesel fuel engine. The engine includes a VGTsystem for providing pressurized intake air to the plurality ofcylinders. VGT turbine 12, compressor 14, and cooler 16 compose the VGTsystem. The pressure of the engine exhaust gases causes VGT turbine 12to spin. VGT turbine 12 drives compressor 14. Compressor 14 pressurizesintake air to develop increased power during combustion. Charge aircooler 16 cools the pressurized air. The VGT system has moveablecomponents that can change the turbocharger geometry by changing thearea or areas in the turbine stage to which exhaust gases flow, and/orchanging the angle at which the exhaust gases enter or leave theturbine. The turbocharger supplies varying amounts of turbo boostpressure depending on the turbocharger geometry. The VGT system inembodiments of the present invention may take any suitable form. Forexample, a variable inlet nozzle to the turbine, a moveable sidewall inthe turbine housing, or any other controllable air pressurizng deviceincluding the above examples, and including a modulated wastegate valvemay compose the VGT system.

EGR valve 18 and cooler 20 compose the EGR system. The EGR systemintroduces a metered portion of the exhaust gases into the intakemanifold. The exhaust gases lower combustion temperatures to reduce thelevel of oxides of nitrogen (NO_(x)) that are produced. In embodimentsof the present invention, the EGR system may take any suitable form. Forexample, a butterfly valve is a suitable EGR valve.

With continuing reference to FIG. 1, the engine also includes acontroller 22. Controller 22 communicates with the VGT system and theEGR system to control the engine. Controller 22 may take any suitableform. A suitable controller includes a programmed microprocessor. Inoperation, controller 22 receives signals from the various vehicle andengine sensors and executes programmed logic embedded in hardware and/orsoftware to control the engine.

Generally, the VGT system provides pressurized intake air to the enginecylinders, and the EGR system provides a metered portion of the exhaustgases to the engine cylinders. The turbo boost pressure results inincreased power while the introduction of exhaust gases lowerscombustion temperatures. Controller 22 operates the engine and controlsthe VGT system and EGR system in accordance with the current engineoperating mode which is based on any number of engine conditions. Duringmodes that require EGR, EGR flow rate is controlled by controller 22issuing commands to EGR valve 18. FIGS. 2-4 illustrate EGR valve controlin the preferred embodiment.

At block 30, an air mass flow rate through the intake manifold isdetermined at a location upstream of the exhaust gas introduction.Specifically, an air mass flow sensor at the compressor inlet measuresthe fresh charge air flow. The air mass flow sensor may be hot-wire orhot-film based. Because the compressor inlet flow is quite stable,accurate measurement can be readily obtained. At the same time, theengine volumetric efficiency can be mapped for various engine operatingconditions. Volumetric efficiency is the ratio of effective enginedisplacement volume to total engine displacement volume. In general, thevolumetric efficiency mapping can be established as a function of enginespeed and intake manifold density. Intake manifold density is a functionof intake manifold pressure and temperature. Engine speed, intakemanifold air density, and volumetric efficiency are determined at blocks32, 34, and 36, respectively. Some corrections can be applied to accountfor other factors such as engine exhaust to intake pressure ratio. Themapping can be accomplished via a look-up table of intake manifolddensity and engine speed. Block 50 illustrates determining an engineexhaust to intake pressure ratio. Block 52 illustrates determining acorrection factor based on the engine exhaust to intake pressure ratio,with the engine volumetric efficiency being further based on thecorrection factor. As an alternative, a neural network model can bebuilt to map the volumetric efficiency as a function of multiplevariables including engine speed, intake manifold pressure andtemperature, exhaust manifold pressure, or turbocharger geometry, etc.Establishing a neural network that receives a number of inputs andprovides the engine volumetric efficiency as an output is indicated atblock 60.

With the fresh charge flow measured and engine volumetric efficiencymapped, the EGR flow rate can be determined as follows:

{dot over (m)} _(EGR)=η_(v)ρ_(a,i) V _(d) N/2−{dot over (m)} _(charge)

where η_(v) is the engine volumetric efficiency, ρ_(a,i) is the intakemanifold air density, V_(d) is the engine displacement volume, N is theengine speed, {dot over (m)}_(charge) is the intake manifold air massflow rate, and {dot over (m)}_(EGR) is the EGR flow rate.

With continuing reference to FIG. 2, EGR flow rate is determined atblock 38. The engine is controlled based on EGR flow rate at block 40.

The preferred embodiment of the present invention has several advantagesover the existing direct measurement EGR flow rate techniques. First,the preferred embodiment can improve the accuracy of EGR flow ratebecause the fresh charge flow rate can be accurately measured in thestable flow stream at the compressor inlet, and the volumetricefficiency can be accurately mapped with look-up tables and/or neuralnetwork models based on test data. Second, the preferred embodiment canimprove engine performance because of lower EGR circuit restriction dueto the absence of orifice or venturi-type EGR flow meters. The hot-wireor hot-film fresh charge air flow meter in the preferred embodimentposes very little restriction in the charge air flow path. Third, in thepreferred embodiment, not using a pressure measurement based flow meter(orifice or venturi) in the EGR circuit reduces sensor malfunctionpossibilities and potential warranty costs for the engine manufacturer.

While embodiments of the invention have been illustrated and described,it is not intended that these embodiments illustrate and describe allpossible forms of the invention. Rather, the words used in thespecification are words of description rather than limitation, and it isunderstood that various changes may be made without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method for controlling an internal combustionengine, the engine including an engine block defining a plurality ofcylinders, an intake manifold for supplying air to the plurality ofcylinders, a controller, and an exhaust gas recirculation (EGR) system,the EGR system introducing a metered portion of exhaust gases to theintake manifold, the controller communicating with the EGR system tocontrol the engine, the method comprising: determining an air mass flowrate through the intake manifold at a location upstream of the exhaustgas introduction; determining an engine speed; determining an intakemanifold air density; determining an engine volumetric efficiency basedon the engine speed and the intake manifold air density; determining anEGR flow rate based on the volumetric efficiency, the intake manifoldair density, an engine displacement volume, the engine speed, and theintake manifold air mass flow rate; and controlling the engine based onthe EGR flow rate.
 2. The method of claim 1 wherein determining theengine volumetric efficiency further comprises: determining an engineexhaust to intake pressure ratio; and determining a correction factorbased on the engine exhaust to intake pressure ratio, wherein the enginevolumetric efficiency is further based on the correction factor.
 3. Themethod of claim 1 wherein determining the engine volumetric efficiencyfurther comprises: establishing a neural network that receives theengine speed, an intake manifold air pressure, an intake manifold airtemperature, and an exhaust pressure as inputs, and provides the enginevolumetric efficiency as an output.
 4. The method of claim 1 whereindetermining the EGR flow rate further comprises: determining the EGRflow rate according to {dot over (m)} _(EGR)=η_(v)ρ_(a,i) V _(d)N/2−{dot over (m)} _(charge) where η_(v) is the engine volumetricefficiency, ρ_(a,i) is the intake manifold air density, V_(d) is theengine displacement volume, N is the engine speed, {dot over(m)}_(charge) is the intake manifold air mass flow rate, and {dot over(m)}_(EGR) is the EGR flow rate.
 5. An internal combustion engine, theengine including an engine block defining a plurality of cylinders, anintake manifold for supplying air to the plurality of cylinders, acontroller, and an exhaust gas recirculation (EGR) system, the EGRsystem introducing a metered portion of exhaust gases to the intakemanifold, the controller communicating with the EGR system to controlthe engine, the controller being programmed to control the internalcombustion engine by: determining an air mass flow rate through theintake manifold at a location upstream of the exhaust gas introduction;determining an engine speed; determining an intake manifold air density;determining an engine volumetric efficiency based on the engine speedand the intake manifold air density; determining an EGR flow rate basedon the volumetric efficiency, the intake manifold air density, an enginedisplacement volume, the engine speed, and the intake manifold air massflow rate; and controlling the engine based on the EGR flow rate.
 6. Theengine of claim 5 wherein determining the engine volumetric efficiencyfurther comprises: determining an engine exhaust to intake pressureratio; and determining a correction factor based on the engine exhaustto intake pressure ratio, wherein the engine volumetric efficiency isfiercer based on the correction factor.
 7. The engine of claim 5 whereindetermining the engine volumetric efficiency further comprises:establishing a neural network that receives the engine speed, an intakemanifold air pressure, an intake manifold air temperature, and anexhaust pressure as inputs, and provides the engine volumetricefficiency as an output.
 8. The engine of claim 5 wherein determiningthe EGR flow rate further comprises: determining the EGR flow rateaccording to {dot over (m)} _(EGR)=η_(v)ρ_(a,i) V _(d) N/2−{dot over(m)} _(charge) where η_(v) is the engine volumetric efficiency, ρ_(a,i)is the intake manifold air density, V_(d) is the engine displacementvolume, N is the engine speed, {dot over (m)}_(charge) is the intakemanifold air mass flow rate, and {dot over (m)}_(EGR) is the EGR flowrate.